The present invention relates to the general field of systems for inducing controlled force into a filament. More particularly, the present invention is directed to a force-inducing device utilizing a pressurized fluid to impart a drag force on a filament, thereby inducing a longitudinal force into the filament.
Electric discharge machining (EDM) involves the use of a high-frequency electrical spark discharged from a metal tool serving as an electrode to disintegrate regions of a workpiece made of an electrically conductive material, such as hardened steel or carbide. The electrode and workpiece are immersed in a dielectric fluid, and a feed mechanism maintains a spark gap, typically from 0.013 mm to 0.5 mm, between the electrode and workpiece. As the spark discharges, it melts and vaporizes small particles of the workpiece. The particles are flushed away and the electrode is advanced to a new location where another spark is discharged. EDM is accurate and may be used for machining dies, molds, holes, slots or cavities of almost any desired shape. In traveling wire EDM, a small diameter wire is used as the tool for cutting out two- and three-dimensional fretwork profiles.
Present traveling-wire EDM systems use pinch roller and mechanical or electrical clutches to advance the wire and control the tension in the wire. This approach is acceptable for wire having a diameter of greater than 100 microns, but is not suited for wire of smaller diameter. Small diameter wire quickly wears grooves into the pinch rollers, causing the wire to slip and requiring frequent replacement of the rollers. In addition, the relatively low levels of tension, typically on the order of grams and fractions of a gram, required when using small diameter wire are difficult to control with present clutch systems. It is also difficult to rapidly stop and start the advancement of the wire due to the relatively large inertial mass of the pinch roller systems. Moreover, stress concentrations within the wire caused by localized contact between the wire and the rollers causes frequent rupturing of the wire and, therefore, undesirable system downtime while the ruptured wire is replaced and/or re-threaded.
For the foregoing reasons, commercial traveling-wire EDM systems are practically limited to wire having diameters greater than 100 microns. However, it is desirable to use smaller diameter wires in EDM systems to reduce the minimum feature size to which a workpiece may be machined. A smaller diameter wire would concentrate the electrical discharge into a smaller region and, thus, allow for more precise disintegration of the material removed from the workpiece. In addition, it is necessary to maintain the wire at as large a tension as possible to increase the precision of the EDM system. The electrical discharge between the and the workpiece induces vibration into the wire that tends to increase the width of the kerf cut by the wire. However, the more taught the wire, the smaller the amplitude of the vibration and the higher the precision of the cut. Present pinch roller and clutch systems can not provide the level of tension desired for wires less than 100 microns due to the problems associated with such systems noted above.
The present invention is directed to a device for inducing a force into a filament. The device includes an enclosure that defines a chamber and comprises a first orifice, a second orifice, a sidewall and a fluid inlet. The first orifice, second orifice and fluid inlet are each in fluid communication with the chamber. The first orifice has an area, and the second orifice defines a passageway having a transverse cross-sectional area larger than the area of the first orifice. Each of the first and second orifices are for receiving the filament. The sidewall has an inner surface located radially outward from a line extending between the first and second orifices. The fluid inlet is located non-tangentially to the inner surface of the sidewall.
In another aspect, the present invention is directed to a system for applying a force to a filament. The system comprises at least two devices, each device for applying an incremental force to the filament. Each device includes an enclosure that defines a chamber for receiving the filament. The enclosure includes a first orifice in fluid communication with the chamber and having a longitudinal axis and a cross-sectional area transverse to said longitudinal axis, the first orifice for receiving the filament. The enclosure also includes a second orifice in fluid communication with the chamber and defining a passageway having a diameter, a length, and a cross-sectional area transverse to the length larger than the cross-sectional area of the first orifice, the second orifice for receiving the filament. The enclosure further includes a fluid inlet in fluid communication with the chamber, the fluid inlet for supplying fluid to said chamber. The devices are located in series with one another such that the incremental forces applied to the filament by said at least two devices are applied in the same direction as one another.
In yet another aspect, the invention is directed to a device for applying a force to a filament. The device includes an enclosure and an elongate body. The enclosure defines a chamber for receiving the filament and comprises a first orifice, a second orifice and a fluid inlet, each of which is in fluid communication with the chamber. The first orifice has an area, and the second orifice defines a passageway having a transverse cross-sectional area larger than the area of the first orifice. Each of the first and second orifices are for receiving the filament. The fluid inlet is for supplying fluid to the chamber. The elongate body is located outside the chamber and the passageway extends within the elongate body.
The present invention is also directed to a method of inducing a longitudinal force into a filament. First, an enclosure is provided. The enclosure defines a chamber and has a first orifice and a second orifice each in fluid communication with the chamber. The first orifice has an area, and the second orifice has an area greater that the area of the first orifice. Next, a filament is threaded through the first orifice, chamber and second orifice. A fluid is flowed into the chamber such that the fluid is under pressure relative to an ambient pressure surrounding the enclosure and the filament is substantially linear between the first and second orifices.